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Stock-Based Compensation (Assumptions Used to Determine Fair Value of Options) (Details)	12 Months Ended
	May 31, 2013	May 31, 2012	May 31, 2011
Share-based Compensation [Abstract]
Risk-free interest rate	1.30%	2.40%	2.50%
Dividend yield	1.80%	1.70%	1.50%
Expected volatility of Cintas' common stock	28.00%	28.00%	30.00%
Expected life of the option in years (years)	7 years 6 months	7 years 6 months	7 years 6 months

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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